On the Origin and Evolution of Three Dimensional Effects in the Mixing Layer
Abstract
There seems to be at least two different phenomena connected with the three-dimensional breakdown of the plane mixing layer. First, at least in some cases, there is a macroscopic instability of the large structure which produces a spanwise system of longitudinal jets whose amplitude builds up very quickly and then remains approximately constant while their separation adjust itself to a value that is somewhat higher that the vorticity thickness of the layer. This phenomenon may be due to a collective instability of the vortex cores of the same type as the one found in vortex rings. The second phenomenon is the development of a 3-D inertial subrange in the spectrum of the small scales of the velocity fluctuations. In the only case in which we have documented both phenomena the second one does not develop fully until the macroscopic instability has not been growing for some time and has actually arrived to what seems to be its final configuration. Moreover there is some indication that there are two qualitatively different ways for the establishment of the 3-D inertial ranges, exemplified here by the water and air experiments. In the first one the transition is abrupt and there is an initial part in which the inertial range has a slope characteristic of the 2-D entrophy cascade. In the second one the transition is more gradual and there is no evidence of a 2-D regime. It is not clear at present which is the condition responsible for the differences between the two cases. The work presented in this report should be seen as a preliminary exploration of the effects connected with the 3-D transition. Much more research is needed in all cases.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1979
- Accession Number
- ADA096007
Entities
People
- Javier Jimenez
- Manuel Rebollo
- Rodrigo Martinez-val
Organizations
- Technical University of Madrid